Simplifications of the mixing algorithm.

webrtc/modules/audio_mixer/test/audio_mixer_unittest.cc

Index: webrtc/modules/audio_mixer/test/audio_mixer_unittest.cc
diff --git a/webrtc/modules/audio_mixer/test/audio_mixer_unittest.cc b/webrtc/modules/audio_mixer/test/audio_mixer_unittest.cc
index 9a51e911f7202b193abb50e4ccc73042c759383c..fdb38b7ee45337923ee2f7cf2597e0535ba898c3 100644
--- a/webrtc/modules/audio_mixer/test/audio_mixer_unittest.cc
+++ b/webrtc/modules/audio_mixer/test/audio_mixer_unittest.cc
@@ -272,6 +272,8 @@ TEST(AudioMixer, ParticipantSampleRate) {
   for (auto frequency : {8000, 16000, 32000, 48000}) {
     EXPECT_CALL(participant, GetAudioFrameWithMuted(_, frequency))
         .Times(Exactly(1));
+    participant.fake_frame()->sample_rate_hz_ = frequency;
+    participant.fake_frame()->samples_per_channel_ = frequency / 100;
     mixer->Mix(frequency, 1, &frame_for_mixing);
     EXPECT_EQ(frequency, frame_for_mixing.sample_rate_hz_);
   }